Abstract Two‐day‐old maize seedlings were incubated in the presence or absence of 1 mM spermidine in the external medium. After 2 h, an increase of potassium (K+) efflux from roots was observed in treated seedlings up to a maximum after a 4 h treatment, decreasing to control values in the following hours. Simultaneously, an inhibition of K+ uptake occurred in roots from treated seedlings up to minimum values after 7–9 h treatment. Successively, roots from treated seedlings progressively recovered their K+ uptake capacity up to values about 50% higher than control seedlings. No variations in K+ content were observed after 24 h between control and spermidine‐treated seedlings taken as a whole, while the K+ content of roots and shoots showed different values when individually analysed. Our results suggest that for spermidine‐treated plants, the K+ content is mantained constant after 24 h by an equilibrium of the influx/efflux systems while a different K+ content in shoots and roots is related to a different growth rate induced by the presence of spermidine in the external medium.